ELECTROWEAK RADIATIVE-CORRECTIONS TO T-]BW FOR A HEAVY TOP

Leading one-loop electroweak radiative corrections to t --> bW are calculated for a heavy top. For a sufficiently large top mass m(t), the calculation of the amplitude is greatly simplified since, in 't Hooft-Feynman gauge, the term of leading order in m(t) comes from only two vertex diagrams (plus quark wavefunction renormalization constants). This calculation also gives the leading dependence of the amplitude on the physical Higgs mass m(H). All our results are gauge-independent. The leading diagrams are of O(m(t)2/m(w)2) relative to the tree-level amplitude, due to scalar-field-top-quark couplings. The magnitude of the correction to the tree-level width is less-than-or-similar-to 1% for m(t) less-than-or-similar-to 200 GeV and 25 GeV less-than-or-similar-to m(H) less-than-or-similar-to 1 TeV.